1. Field of Invention
The present invention relates to a method of reworking a semiconductor device. More particularly, the present invention relates to a method of using a low-temperature plasma treatment to remove a photoresist layer.
2. Description of Related Art
Photolithography is often regarded a critical step in the fabrication of semiconductor devices. In the fabrication of MOS device structures, anything from the patterning of thin films to dopants implants involves photolithographic processes. Following the rapid increase in the level of integration for integrated circuits, dimensions of each semiconductor device are reduced. With a corresponding reduction in line width, photolithographic process has become complicated and difficult. To increase production yield, a bottom anti-reflection coating is formed over a substrate before deposition photoresist material on top. Such an arrangement can reduce standing wave and halftone during exposure so that more accurate pattern is transferred.
After photoresist development, quality of the photoresist layer is usually inspected, the so-called after development inspection (ADI) before the next photolithographic step is executed. When misalignment or other types of errors is found in the photoresist pattern, the photoresist layer must be reworked to prevent permanent damage to the entire batch of chips in subsequent processes.
Conventional method of reworking the photoresist layer includes removing the incorrectly developed photoresist layer from the silicon chip by wet etching. Since the photoresist layer has already been cured and bombarded by electron beam, wet etching can hardly remove every bit of the photoresist layer. Consequently, oxygen plasma is often employed to remove the hardened photoresist layer. Thereafter, a new photoresist layer is formed over the silicon chip followed by subsequent exposure and resist development.
However, most bottom anti-reflection coating contains silicon oxynitride (SiON) aside from organic material. Since silicon oxynitride has a rather unstable chemical structure, especially when heated to a temperature above 150xc2x0 C., the silicon oxynitride may turn into silicon oxide.
Because conventional oxygen plasma treatment is conducted at a temperature above 200xc2x0 C., the silicon oxynitride material inside the anti-reflection coating is likely to transform into silicon oxide. In general, light absorption or attenuation capacity of a silicon oxynitride layer is affected by its silicon oxide content. In other words, reflectivity of the silicon oxynitride layer will increase leading to a deterioration of anti-reflection capacity. Hence, after using a conventional oxygen plasma treatment to remove photoresist layer, the newly formed photoresist layer on the reworked surface will have a lower capacity to reproduce critical dimensions due to an increase in reflectivity for the anti-reflection coating. In other words, quality of the reworked photoresist pattern is likely to drop.
Accordingly, one object of the present invention is to provide a method of reworking a photoresist layer capable of preventing a drop in anti-reflection capacity of a silicon oxynitride layer.
A second object of the invention is to provide a method of reworking a photoresist layer capable of preventing a reduction in the critical dimensions of a subsequently formed photoresist layer.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of reworking a photoresist layer. A silicon chip having an insulation layer, a bottom anti-reflection coating and a photoresist layer thereon is provided. The photoresist layer has already been light-exposed and developed. A wet etching operation is carried out to remove a large portion of the photoresist layer. A low-temperature plasma treatment incapable of transforming the anti-reflection coating structure is conducted to remove the hardened residual photoresist material. Finally, a new photoresist layer is formed over the bottom anti-reflection coating.
One major aspect of this invention is the use of a low-temperature plasma treatment to remove residual photoresist material after wet etching so that the bottom anti-reflection coating can maintain its anti-reflection capacity. Since the silicon oxynitride material within the anti-reflection layer is heated to a relatively low temperature in the plasma treatment, the rate of transformation of silicon oxynitride into silicon oxide is low. Hence, anti-reflection capacity of the bottom anti-reflection coating is retained after reworking.
In addition, the maintenance of anti-reflection capacity after plasma treatment helps to preserve the critical dimensions of the newly deposited photoresist layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.